1. Field of the Invention
The present invention relates generally to a display panel, a method of manufacturing a display substrate of the panel, and a mask for implementing the manufacturing method. More particularly, the present invention relates to a display substrate capable of reducing defects that may otherwise be generated during the manufacturing process thereof, a method of manufacturing the display substrate, which is capable of regulating the thickness of a photoresist pattern formed through a three-mask process, and a mask for implementing the method.
2. Description of the Related Art
In general, signal lines, thin film transistors and pixel electrodes formed on a display substrate are patterned through a photolithography process using a mask. In the manufacture of display substrates, the ability to reduce the number of photolithography process used leads to a beneficial reduction in manufacturing costs. One way to reduce such costs in manufacturing a display substrate is by using three sheets of mask in what is known as a three-mask process.
For example, in a three-mask process, after signal lines and thin film transistors are formed on a substrate through a photolithography process using first and second masks, a passivation layer is then formed on the substrate. Sequentially, a photoresist pattern is formed on the passivation layer through another photolithography process using a third mask. The photoresist pattern overlaps the signal lines and the thin film transistors. The photoresist pattern is used for etching the passivation layer once or twice and for patterning pixel electrodes in a lift-off method.
In the event etching processes using the same photoresist pattern are performed twice, defects induced by over-etching of lower thin films may be generated. Therefore, it is important that the photoresist pattern is disposed over the entire substrate, and at a uniform thickness.
However, because the density of a photoresist pattern formed over a display substrate is typically varies from region to region, the amount of photoresist that melts during a developing process also varies from region to region.
For example, when the density of the photoresist pattern is relatively low, the amount of photoresist melt during developing of the photoresist pattern is relatively large. Moreover, in regions having low photoresist density, the acid concentration of developing solution spread on the low density regions rapidly dwindles. Thus, a concentration difference between a region having low density and a region having high density results. In turn, portions of the developing solution having a high concentration migrate to the developing solution having a low concentration. Therefore, the photoresist pattern in the low density regions becomes over developed with respect to the desired amount, resulting in an irregular thickness of the photoresist pattern.